@jgrmpf, What do you want to do with the R5 core?
If you want to do a baremetal MCU to control I/O you need to review the board schematics and the TRM. This will let you know what to study. Also, review all the BBAI64 R5F examples that the community has posted. For baremetal, Learn about ARMv7 and newlib. For peirpherials, study the TRM and the TI libraries.
@foxsquirrel, For the BBAI64 Using TI libraries to control GPIO example that @ewaldhr linked above. Use the firmware from here ARM64 - Debian 12.x (Bookworm) - Monthly Snapshots - 2023-10-07. Debian 12 with kernel 5.10. That example uses the TI CSL layer to access the periperials. If you use firmware 6.1 or later, the examples don’t work because the layout of some stuff has moved around.